Understand PCB stackup in one article

Forward to previous one

3.Three, six-layer laminate

For designs with higher chip density and higher clock frequency,a 6-layer board design should be considered,and the stacking method is recommended:

1.SIG－GND－SIG－PWR－GND－SIG;

For this kind of scheme, this kind of laminated scheme can get better signal integrity, the signal layer is adjacent to the ground layer, the power layer and the ground layer are paired, the impedance of each wiring layer can be better controlled, and The stratum can absorb the magnetic field lines well.And when the power supply and ground layer are intact, it can provide a better return path for each signal layer.

2.GND－SIG－GND－PWR－SIG －GND;

For this kind of scheme,this kind of scheme is only suitable for the situation that the device density is not very high, this kind of lamination has all the advantages of the upper lamination,and the ground plane of the top and bottom layers is relatively complete,which can be used as a better shielding layer To use. It should be noted that the power layer should be close to the layer that is not the main component surface, because the plane of the bottom layer will be more complete. Therefore, EMI performance is better than the first solution.

Summary:For the six-layer board scheme, the distance between the power layer and the ground layer should be minimized to obtain good power and ground coupling.However,although the thickness of the board is 62mil and the layer spacing is reduced, it is not easy to control the spacing between the main power supply and the ground layer to be small.Comparing the first scheme with the second scheme, the cost of the second scheme will increase greatly. Therefore, we usually choose the first option when stacking. When designing, follow the 20H rule and the mirror layer rule design.

4.Four and eight-layer laminates

1) This is not a good stacking method due to poor electromagnetic absorption and large power supply impedance.Its structure is as follows:

1.Signal 1 component surface, microstrip wiring layer

2.Signal 2 internal microstrip wiring layer, better wiring layer (X direction)

3.Ground

4.Signal 3 stripline routing layer, better routing layer (Y direction)

5.Signal 4 stripline routing layer

6.Power

7.Signal 5 internal microstrip wiring layer

8.Signal 6 microstrip trace layer

2) It is a variant of the third stacking method. Due to the addition of the reference layer, it has better EMI performance, and the characteristic impedance of each signal layer can be well controlled

1.Signal 1 component surface,microstrip wiring layer,good wiring layer

2.Ground stratum,good electromagnetic wave absorption ability

3.Signal 2 strip line routing layer,good routing layer

4.The Power layer forms excellent electromagnetic absorption with the ground layer below.

5.Ground layer

6.Signal 3 stripline routing layer,good routing layer

7.Power stratum,with large power supply impedance

8.Signal 4 microstrip wiring layer,good wiring layer

3) The best stacking method, due to the use of multiple ground reference planes, it has very good geomagnetic absorption capacity.

1.Signal 1 component surface,microstrip wiring layer,good wiring layer

2.Ground stratum, good electromagnetic wave absorption ability

3.Signal 2 strip line routing layer,good routing layer

4.The Power layer forms excellent electromagnetic absorption with the ground layer below.

5.Ground layer

6.Signal 3 strip line routing layer,good routing layer

7.Ground stratum,better electromagnetic wave absorption ability

8.Signal 4 microstrip wiring layer,good wiring layer

How to choose how many layers of boards are used in the design and how to stack them depends on many factors such as the number of signal networks on the board, device density,PIN density,signal frequency, board size and so on.For these factors,we must comprehensively consider.For the more signal networks,the higher the device density, the higher the PIN density and the higher the signal frequency, the multilayer board design should be adopted as much as possible.To get good EMI performance,it is best to ensure that each signal layer has its own reference layer.

Source: Fanyi PCB